Presbyopia is a vision condition wherein the eye has a progressively reduced ability to focus on nearby objects. It is typically thought to arise from a loss of flexibility of the lens within the eye. Presbyopia affects the majority of human beings as they age, typically becoming noticeable when a person reaches their mid-forties.
Presbyopia, by itself, can be corrected in a straightforward manner using corrective eyeglasses, such as reading glasses. When a person is afflicted with both presbyopia and another condition that requires the use of corrective eyeglasses (e.g., myopia), however, vision correction becomes more complicated.
The most common prior-art correction for presbyopia in a patient that requires eyeglasses for another condition involves eyeglass lenses with different focal lengths in different areas of the lens. Examples of such lenses include “bifocals,” which incorporate two different focal-length regions, “trifocals,” which incorporate three different focal-length regions, and “progressive lenses,” which incorporate a continuum of focal lengths. Typically, the lower part of these lenses incorporates the shorter focal length region allowing focus on near objects in the lower part of the field of view.
Unfortunately, such an optical configuration does not support focusing on nearby objects in the middle or upper part of the field of view. As a result, the eyeglass wearer must tilt their head backward to clearly see a nearby object located directly in front of the face. Often, the required tilt angle leads to patient discomfort.
Further, for progressive lens designs, it is normally necessary to make compromises that give rise to a significantly reduced width of the in-focus field of view at near distances.
In another prior-art approach for correction of presbyopia, eyeglass frames include deformable lenses whose shape is fluidically controlled. Each lens comprises a fluid that is encapsulated either between two deformable transparent membranes or a single deformable membrane and a rigid lens or plate. The shape of the lens is controlled by pumping the fluid into or out of the cavity of each lens.
Unfortunately, it is difficult to control of the membrane deformation to avoid gross distortion of the image. Typically, the lens shape is restricted to circular, since circular lenses tend to deform in a radially symmetric fashion. The need for circular lenses, however, is undesirable as many eyeglass wearers do not wish to be constrained to round lenses.
In addition, membrane deformation systems require one or more fluid reservoirs, as well as pump systems for pumping fluid in and out of the lens cavities to control their focal lengths. These pumping systems add weight and bulk to the eyeglass frames making them less comfortable for the user—particularly when worn for long periods of time. Further, the style and attractiveness of eyewear is strongly dependent on the design of their frames. Requiring fluid reservoirs and/or pumps in the frames limits the eyewear design space and can dramatically detract from their look and marketability.
An eyeglass system having lenses whose focal length is controllable across their entire clear aperture, can have any desired lens shape, and retain a broad design space for eyewear frames, would be a significant advance in the state-of-the-art of vision correction.